Beta lactones are a class of chemical compounds that have great industrial potential
For example, beta lactones (e.g., beta propiolactone (BPL)) can undergo reactions to produce valued chemical derivatives, including 3-hydroxypropionic acid and its esters, propanediol, acrylic acid, acrylate esters and amides, succinic anhydride, succinic acid, butanediol, polypropiolactone biodegradable polymers, and others. It also has some industrial uses itself as a specialty disinfectant to sterilize medical products.
However, since beta propiolactone has been difficult to manufacture in a selective and high yielding fashion and because it has been found to be a probable human carcinogen, the use of this highly interesting and reactive chemical intermediate is limited. Some previous commercial applications which otherwise represented economically attractive processes, such as the manufacture of acrylic acid and its esters, have been phased out in favor of other alternatives. In the case of acrylic acid manufacture, the industry has turned to propylene oxidation. For many years propylene was a low cost feedstock and alternate routes to acrylic acid were of little interest. However because propylene production is tightly tied to petroleum refining its price fluctuates with crude oil prices. Propylene availability is further impacted by demands for other product in the refiningetroleum industry. As a result propylene prices have risen sharply in recent years. This dynamic has prompted interest in alternate routes to acrylic acid. The use of ethylene oxide (EO) as a feedstock for acrylic acid is increasingly attractive since EO can be derived from inexpensive ethylene sourced from natural gas production. Carbonylation of EO can provide beta propiolactone in excellent yield and selectivity, however the problems of handling and transporting this toxic chemical still remain.
In order to take advantage of the unique chemical properties of beta propiolactone, which is just one example of the class of similar lactones which includes beta butyrolactone and other interesting lactone chemical intermediates, it is desired to develop integrated processes in which the purification or isolation of beta propiolactone is avoided.
It is therefore a broad object of this invention to provide the integrated production and conversion of beta lactones, without their intermediate separation, with the aim of avoiding the potential exposure to the hazards of some of the class of lactones, while at the same time providing economically advantageous production processes.
Commercially, beta propiolactone has in the past been produced by the reaction of ketene with formaldehyde. The production of ketene is based on the high temperature (700-750° C.) thermal dissociation of acetic acid in the presence of triethyl phosphate under a reduced pressure. This ketene process is mechanically complex, highly energy intensive and is a source of unwanted emissions to the atmosphere. After isolation, highly reactive monomeric ketene can be reacted with aldehydes to form beta lactones in the presence of aluminum chloride catalyst, commonly referred to as a Friedal-Crafts catalyst.
Reaction of ketene and formaldehyde yields beta propiolactone. Reaction with acetaldehyde produces beta butyrolactone, while reaction with crotonaldehyde forms a polyester which is then thermally decomposed to sorbic acid. The aluminum chloride itself has many hazards it use, including potentially violent reactions of anhydrous aluminum chloride with water or bases. This very active catalyst also results in the formation of a number of unwanted byproducts that must be separated and removed from the desired lactone product leading to further handling challenges and additional opportunities for worker exposure. A general problem with the use of aluminum chloride Friedal-Crafts catalyst is that it is often consumed in the reaction, is very difficult to recover and regenerate, and commonly must be destroyed after use, generating a large amount of corrosive waste.
Therefore, it is advantageous to rely on a better process for the production of beta lactones, and more particularly the intermediate, beta propiolactone, by the carbonylation of the corresponding epoxide, particularly ethylene oxide in the case of beta propiolactone.